Temp Gauge Bad?

[Philn]

On my 2002 60hp merc outboard, the temp guage doesn't work.

Per a previous thread, I applied 12v to gauge and it pegged all the way to the right as it should.

Reconnected the sender wire and turned on the ignition. Checked voltage at the sender terminal on the gauge and had 9.5v, engine cold. When engine warmed up voltage at gauge sender was 11.5. Needle had not moved at all.
Bad gauge?
Does the gauge sender run on voltage or should I be measuring impedence (ohms)???

Thanks in advance for any help.

 

[john from md]

Re: Temp Gauge Bad?

Take the sensor and attach it to an ohm meter. You will have to experiment with what scale to use. Heat it with a propane match and watch for resistance changes. If the meter gives steady movement accross the scale, the sensor is ok.

Make sure you have a good ground on the meter. If the ground has corrosion, it will cause high resistance and the meter won't function. You can check this by connecting a alligator clip jumper from the gauge to a good ground.

Hope this helps.

John

 

[Silvertip]

Re: Temp Gauge Bad?

Your temp guage uses both voltage and resistance -- actually varying resistance from heat changes results in varying voltage applied to the sender terminal on the gauge which causes the meter to move. Disconnect the sender wire at the sender or the gauge and measure the resistance (1000 ohm scale). On a stone cold engine the resistance should read somewhere near 240 ohms. On the hot side (212 degrees) it should measure about 33 ohms. I would not use a propane lighter and direct heat on the sender as it may get too hot. Dip the sender (just the tip) in a pan of water on the stove and watch the meter as the water heats up.